The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The ongoing quest for higher storage bit densities in magnetic media used in disk drives have reduced the size (volume) of data cells to the point where the cell dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, there is concern that data stored within the cells is no longer thermally stable, as random thermal fluctuations at ambient temperatures are sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or lowering the temperature. Lowering the temperature is not a practical option when designing hard disk drives for commercial and consumer use. Raising the coercivity is a practical solution, but requires write heads employing higher magnetic moment materials, or techniques such as perpendicular recording (or both).
One additional solution has been proposed, which employs heat to lower the effective coercivity of a localized region on the magnetic media surface and writes data within this heated region. The data state becomes “fixed” upon cooling the media to ambient temperatures. This technique is broadly referred to as “thermally assisted (magnetic) recording”, TAR or TAMR. It can be applied to both longitudinal or perpendicular recording systems, although the highest density state of the art storage systems are more likely to be perpendicular recording systems. Heating of the media surface has been accomplished by a number of techniques such as focused laser beams or near field optical sources.
U.S. Pat. No. 6,999,384 to Stancil et al., which is herein incorporated by reference, discloses near field heating of a magnetic medium.
Unfortunately, there are several disadvantages to known laser-based systems. For example, as shown in FIG. 21, taken from U.S. Pat. No. 6,778,582 which is herein incorporated by reference for its disclosure of the principles of laser construction and operation, a VCSEL (vertical cavity surface emitting laser), which as shown is a three mirror VCSEL where the third mirror is on the backside of the wafer. This means that the thickness of the semiconductor wafer (such as GaAs based material) forms an external cavity for the VCSEL. The external cavity allows for higher single mode power than can be reached with a typical VCSEL without the external cavity and third mirror. In such prior art designs, the light is emitted from the top, away from the mount. The top mirror is partially reflective and there is an annular contact to the top side. The substrate is doped to allow current to flow from the top contact to the active region. The intermediate mirror, active region, oxide aperture, and highly-reflective bottom mirror are fabricated on the GaAs substrate. The mount provides for the other contact. Because the light is emitted from the top of the laser, device placement is severely limited. Moreover, the opposing position of the contacts makes creating the electrical connections onerous.
An implementation of such a laser is shown in FIG. 22, taken from U.S. Patent Appl. Pub. No. 2008/0002298. As shown in FIG. 22, the VCSEL is mounted to a separate substrate, which is then mounted to bonding pads on the trailing edge of a slider. The heat-sinking and electrical connection of the VCSEL is to the side opposite the light emitting side of the laser, then to the mounting substrate, and then to the bonding pads of the separate substrate. Light from the VCSEL is directed to a split grating coupler fabricated on the slider. The grating couples light into a 2D solid immersion mirror. The polarization of the light leaving the laser is in the cross track direction. Light is delivered by the solid immersion mirror to a lollipop antenna at the air-bearing surface for thermally assisted recording. One disadvantage of this approach is that conventional VCSELs do not have sufficient output power for TAR, thereby apparently rendering the system shown in FIG. 22 inoperable. For example VCSELs typically have a maximum power output of 5 mW. TAR requires output power much higher than 5 mW. 50 mW or higher may be needed for TAR. Another disadvantage is the need for a separate mounting substrate. Finally, the output beam from a conventional VCSEL is very small which makes alignment to the grating more difficult. The spacing between the VCSEL and the grating exacerbates the alignment problem.
What is needed is a way to further improve TAR systems.